This invention relates to a troweling apparatus for applying a protective coating of cement mortar or similar material to the inside surface of a pipe.
It is common for mortar or similar plastic material to be applied to the interior surfaces of pipelines already in place to recondition and protect the interior surfaces of such pipes.
A known type of coating applicator and troweling apparatus is disclosed in U.S. Pat. No. 3,384,940 to Barton. That patent discloses a mortar-dispensing machine which tows a multi-stage frusto-conical trowel. Each trowel in that patent includes a plurality of arcuate leaves which overlap circumferentially to form an expandable troweling edge at the larger and trailing end of the trowel. The first stage trowel is rigidly attached to a support rod extending to the rear of the mortar-dispensing machine. The second stage trowel is pivotally attached by a ball joint to the rear end of the support rod. The first stage trowel performs rough troweling of the mortar coating, and the pivotally-attached second stage performs finish smoothing.
In trowels having overlapping leaves, each overlap between adjacent leaves tends to form tracks or grooves in the coating material after the trowel passes. This is undesirable because the lining operation is intended to provide the smoothest possible surface for minimum friction losses when the lined pipe is placed in service. The purpose of a multi-stage trowel is to provide a second trowel for wiping out any tracks left by the first trowel to obtain the smoothest possible surface. However, the troweling machine in the Barton patent can have difficulty in smoothing tracks left by the first stage, because the pivotally-attached second trowel can rotate relative to the first trowel about an axis through the support rod and end up following the path left by the first trowel.